As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication subsystems transmitting a growing volume of data with a fixed resource such as a fixed channel bandwidth accommodating a fixed data packet size. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each user) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base.
The third generation partnership project long term evolution (“3GPP LTE”) is the name generally used to describe an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communications.
Improvements in bandwidth capacity are being made to cope with continuing new requirements and the growing base of users, and higher data rates and higher system capacity requirements. Goals of this broadly based 3GPP project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards and backwards compatibility with some existing infrastructure that is compliant with earlier standards.
The continuing need for additional spectrum/bandwidth is being addressed in various ways. In one approach to adding broadband spectrum, a transition has been made from analog terrestrial TV broadcast transmission to all digital TV (“DTV”) broadcasting. The DTV signals require substantially less spectrum than the prior analog TV systems, thus freeing the “white space” between DTV transmitters. In the United States, this frequency spectrum is between 54 MHz and 862 MHz. It is possible for this spectrum to be used for broadband wireless communications to provide, for example, wireless voice and high speed internet access in rural areas, and additional broadband communications bandwidth in densely populated or high use areas. However, to use this space correctly, the wireless communications devices must be able to avoid interference with the prior primary users, such as DTV stations, and certain wireless microphones, which are licensed to use the spectrum. To do this the base stations (or NBs) and customer premises equipment (CPEs), whether fixed or portable, must adaptively communicate to avoid introducing interference with the existing transmitters.
A proposed IEEE standard IEEE P802.22, covering Wireless Regional Access Networks (“WRAN”) addresses the use of the “white space”. More information is available from the IEEE working group website at the URL http://www.ieee802.org/22/. The standard addresses the use of the unused “white space” and particularly for adding broadband services for rural areas. A requirement of the WRAN standard is that the new broadband communication devices, such as base stations, do not interfere with existing transmitters using the spectrum. One approach that is developing in the WRAN and other similar systems is the use of cognitive radio transceivers. Cognitive radio devices may effectively use shared spectrum where they must adapt to the presence of other signaling devices (for example existing DTV transmitters, or other primary transmitters using the spectrum), and where blind detection of signals is required. The cognitive radios can identify unknown transmitted signals in the spectrum and by adaptively receiving them, can tune to and communicate with the sending device and create a communications channel. The ability to identify transmitters also makes it possible to avoid interfering with them. That is, the cognitive radios use spectrum sensing to identify transmissions as part of the process of adapting radio frequency communications to the transceivers, and avoiding interference.
Detection of a transmitted signal can be done in a variety of ways. Simple power detection techniques may be used, however, for certain devices such as portable cellular phones, low power transmission levels are used and simple power level detection may not be sufficient to distinguish these transmissions from noise or other possible sources.
A method of spectrum sensing of signals for cognitive radio that has been proposed is the use of cyclostationary based spectrum sensing algorithms, (“CBSSA”). Because signals, including the OFDM/OFDMA signals used for wireless communications, exhibit a periodicity not found in Gaussian noise, it is possible to discriminate such signals from noise by determining whether a cyclostationary property exists with respect to samples of the received signal. However, the CBSSA algorithms known to date require extensive resources including multipliers and large memory storage that make implementation of such algorithms in commercially practicable integrated circuits, such as integrated circuits including ASICs, FPGAs, CPLDs, and the like, impractical.
The wireless communication systems as described herein are applicable to, for instance, wireless communication systems and communications systems, including but not limited to WRAN that could benefit from the use of CBSSA for signal detection.
A need this exists for systems and methods to efficiently provide spectrum sensing of signals using cyclostationary based spectrum sensing algorithms without the disadvantages of the known prior approaches.